A chip-type LED where elements are directly mounted on the pattern of a printed circuit boards and sealed with resin is advantageously used for smaller-sized and lower-profile products; so, it has been used for wide range of electronic devices such as lighting of numerical keypad for cellular phone and back-lighting of small-sized liquid crystal display.
In recent years, technological development of highly bright LED is significant and brightness of the LEDs is becoming higher; with this development, the calorific value of the LED element itself increases and the heat load given at the periphery of the printed circuit boards and so on also is increasing. Therefore, in fact, some LED elements have a periphery temperature of above 100° C. Moreover, in the fabricating process of LED-mounted substrate, thermosetting treatment of sealing resin and lead (Pb)-free solder have been adopted; so, in the reflow step, the LED elements are sometimes exposed under a high heat load environment such as a case of about 260° C. to about 300° C. In such a heat load environment, a conventionally used white printed circuit boards made of a thermoset resin composition tends to show decrease in whiteness due to the discolor into yellow whereby show poor reflection efficiency. Therefore, there is still a room for improvement about future substrates for mounting next-generation highly bright LED. On the other hand, although ceramic substrate is excellent in thermal resistance, due to its hard and brittle properties, there is limitation of using ceramic substrate for a larger-size and lower-profile product; hence, it may become difficult to be used for future general lighting and substrate for display. Accordingly, development of a white printed circuit board, which does not discolor and does not decrease its reflectance under a high heat load but does have a thermal resistance and which is applicable for a larger-sized product, has been required.
To the above issues, Patent document 1 discloses a thermoplastic resin composition comprising 100 parts by mass of a thermoplastic resin, 0.001-10 parts by mass of a specific silicon compound, and 0.05-25 parts by mass of titanium oxide of which average particle diameter is 0.05-1.0 μm and crystalline shape is rutile structure and the surface of which is treated by at least one compound selected from alumina hydrate or hydrated silicates. Patent document 1 states that the molded product made of the thermoplastic resin composition (specifically, a rectangle plate having a size of 100 mm×100 mm×2 mm and being obtained by injection molding of the thermoplastic resin composition) has a reflectance as high as about 90% and exhibits excellent dispersiveness, surface appearance, and mechanical strength, and is suitably used for a wide range of industrial field.
Patent document 2 discloses a reflector, which does not require complex fabricating steps but does show a high reflectance and have a surface roughness of 0.5-50 μm, and which is used for e.g. a lighting and a display device, the reflector comprises a resin composition comprising: a crystalline resin; a white pigment having an average particle diameter of 0.05-5 μm, and an inorganic filler having an average particle diameter of 0.5 μm to 10 mm. The examples thereof may be a rectangle plate having a size of 3 cm×3 cm×1 mm and being obtained by injection molding of a resin composition containing a polyaryl ketone, titanium oxide, and a glass fiber.
In addition, Patent document 3 discloses a polyamide resin composition for forming LED reflector, which comprising: 5-100 parts by mass of titanium oxide; 0.5-30 parts by mass of magnesium hydroxide; and 20-100 parts by mass of reinforcing agent such as fiber-type filler and needle-type filler, based on 100 parts by mass of a specific polyamide resin. Specifically, it shows a plate having a size of 1 mm in thickness, 40 mm in width, and 100 mm in length and being obtained by injection molding of the polyamide resin composition. The reflector made of the resin composition can maintain high whiteness without reducing the reflectance even under a heat load of 170° C. for 2 hours.
Further, Patent document 4 discloses a prepreg comprising a substrate and a resin composition containing a cyanic acid ester compound, novolac-type epoxy resin, and titanium dioxide, and a copper-clad laminate.    Patent Document 1: Japanese Patent No. 3470730    Patent Document 2: Japanese Patent Application Laid-Open (JP-A) No. 2007-218980    Patent Document 3: JP-A No. 2006-257314    Patent Document 4: JP-A No. 2007-131842